Cell membrane IgD is to be analyzed by 1) Cocapping studies using antibodies coupled to different fluorochromes, in cord blood and mouse lymphocytes for possible presence of IgD. 2) Surface iodination techniques in which Ig is extracted with a non-ionic detergent, precipitated with anti-Ig serum and electrophoresed on SDS polyacrylamide gels. A peak of the mobility corresponding to "IgD" will be looked in mouse, rabbit, guinea pig and compared with cord blood.